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  • 1
    Electronic Resource
    Electronic Resource
    Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1691-1693 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122247
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  • 2
    Electronic Resource
    Electronic Resource
    Observation of photoluminescence from Al1−xInxN heteroepitaxial films grown by metalorganic vapor phase epitaxy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 830-831 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed photoluminescence of Al1−xInxN films. The films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. GaN was grown on a c-plane sapphire substrate with a low-temperature deposited AlN buffer layer. Photoluminescence, absorption, and x-ray diffraction measurements have shown that each spectral peak shifts with alloy composition x and that Al1−xInxN heteroepitaxial films are not macroscopically in phase separation and are constituted in the wurzite structure. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122015
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  • 3
    Electronic Resource
    Electronic Resource
    Structural properties of InN on GaN grown by metalorganic vapor-phase epitaxy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 7682-7688 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InN has been expected to be a suitable material for electronic devices such as high mobility transistors because of its small effective mass compared to other nitrides. Heteroepitaxial InN films were grown by metalorganic vapor-phase epitaxy. The films have been structurally characterized by triple-axis x-ray diffraction (XRD) analysis in terms of lattice-mismatch dependence and InN film thickness dependence, and Hall measurements have been performed. In the XRD measurement, ω and ω–2θ scans were used, and the degree of tilting (the linewidth of x-ray signal, Δωc) [(0002) reflection] and that of twisting (Δωa) [(101¯0) reflection] have been separated. In addition, the degree of distribution of lattice constant c (Δ2θc) [(0002) reflection] of InN films has been assessed. For study of the lattice-mismatch dependence, growth of InN films on GaN, AlN and directly on sapphire substrates was performed, and accordingly, Δωc was found to range from about 500 to 4000 arcsec, and Δ2θc from about 400 to 700 arcsec. Among those three kinds of samples, InN films grown on GaN showed the smallest Δωc and Δ2θc values. Observation of c- and a-lattice parameters has shown that the InN on GaN is affected by the residual strain. On the other hand, InN thickness dependence of XRD showed that Δωc was changed from about 700 to 500 arcsec, and Δ2θc from about 600 to 300 arcsec with increasing InN thickness from 400 to 2400 Å. In accordance with the thickness of InN, Δωa was found to change from about 2500 to 1700 arcsec. Moreover, it was found that the InN film less than 1200 Å thick is composed of grain islands with different crystalline orientation and that the growth mode changes at a thickness of about 1200 Å—and screw dislocations occur. It is found that the residual strain in InN films over 1200 Å thick is gradually released, resulting in almost the same orientation. This is reflected in the reduction of the mosaicity, the proceeding of relaxation and the surface morphology. Selection of GaN for the underlying layer of the InN film has been shown to lead to structural improvement of the epitaxial InN film. In fact, InN film with a thickness of 2400 Å grown on GaN has a Hall mobility of about 700 cm2/V s even at an electron carrier concentration of 5×1019 cm−3. This value corresponds to that for GaAs at the same impurity concentration. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370571
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  • 4
    Electronic Resource
    Electronic Resource
    Control of strain in GaN by a combination of H2 and N2 carrier gases (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7820-7824 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the effect of a combination of N2 and H2 carrier gases on the residual strain and crystalline properties of GaN, and we propose its application to the improvement of crystalline quality of GaN/Al0.17Ga0.83N multiple quantum well (MQW) structures. GaN was grown with H2 or N2 carrier gas (H2– or N2–GaN) on an AlN low-temperature-deposited buffer layer. A (0001) sapphire substrate was used. N2–GaN was grown on H2–GaN. The total thickness was set to be 1.5 μm, and the ratio of N2–GaN thickness to the total thickness, x, ranged from 0 to 1. With increasing x, the tensile stress in GaN increased. Photoluminescence intensity at room temperature was much enhanced. Moreover, the crystalline quality of GaN/Al0.17Ga0.83N MQW was much higher when the MQW was grown with N2 on H2–GaN than when it was grown with H2 on H2–GaN. These results were due to the achievement of control of strain in GaN using a combination of N2–GaN and H2–GaN. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371278
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  • 5
    Electronic Resource
    Electronic Resource
    Strain relief and its effect on the properties of GaN using isoelectronic In doping grown by metalorganic vapor phase epitaxy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 4106-4108 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the effect of isoelectronic In doping on the crystalline and optical properties of GaN grown on sapphire with H2 or N2 carrier gas by metalorganic vapor phase epitaxy. The relationship between lattice constants c and a obtained by x-ray diffraction analysis showed that with increasing trimethylindium (TMI) flow during growth, the strain in GaN decreased, and accordingly, the tilting and the twisting components of crystalline mosaicity also decreased. In addition, the Raman shift, the excitonic photoluminescence peak energy, and the its linewidth shifted in accordance with the magnitude and the sign of the strain in GaN, regardless of the carrier gas used. These results revealed that for a smaller TMI flow region, In was incorporated so that the crystallinity of GaN improved, and for a larger TMI flow region, In substituted for Ga so that alloying formation might have occurred. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125551
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical properties of strained AlN/GaN superlattices on GaN grown by metalorganic vapor phase epitaxy (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 802-804 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the temperature dependence of electrical properties of crack-free strained AlN/GaN superlattices (SLs) on GaN grown by metalorganic vapor phase epitaxy. A (0001) sapphire substrate was used. A single AlN on GaN and one and five pairs of AlN/GaN superlattices were grown using N2 carrier gas. The thicknesses of AlN and GaN in the superlattices were 1 and 5 nm, respectively. Hall measurements were performed at 295–20 K. The five pairs of AlN/GaN SLs on GaN showed an electron mobility of 9925 cm2/V s and a sheet carrier density of 1.14×1012 cm−2 at 20 K, and 1354 cm2/V s and 1.14×1012 cm−2 at 295 K. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1446204
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  • 7
    Electronic Resource
    Electronic Resource
    Metalorganic vapor phase epitaxy growth of crack-free AlN on GaN and its application to high-mobility AlN/GaN superlattices (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3062-3064 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have succeeded in growing crack-free AlN of even 0.5 μm thickness on GaN by metalorganic vapor phase epitaxy. A (0001) sapphire substrate was used. Crack-free AlN was grown on GaN at 1000 °C with N2 carrier gas. An AlN layer was grown on GaN of 2 μm thickness grown at 1050 °C, following the low-temperature deposition of an AlN buffer layer of 30 nm. No cracks were observed in the microphotographs of AlN on GaN grown using N2. X-ray diffraction analysis revealed that AlN/GaN superlattices (SLs) were coherently grown on GaN, and satellite peaks up to the third order were observed. The structure of AlN/GaN SLs on GaN showed a maximum electron mobility of 1580 cm2/V s at room temperature and a nominal sheet carrier density of 8.4×1012 cm−2. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1416169
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  • 8
    Electronic Resource
    Electronic Resource
    Anomalous features in the optical properties of Al1−xInxN on GaN grown by metal organic vapor phase epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 876-878 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the optical properties of Al1−xInxN thin films grown on GaN by metal organic vapor phase epitaxy. X-ray diffraction analysis of ω and ω-2θ scans showed that both the compositional fluctuation and the degree of crystalline mosaicity increase with increasing x. While the energy positions of both the absorption edge and photoluminescence peak shift to a lower-energy region with increasing x, the linewidth of the photoluminescence spectra and the value of the absorption edge tail decrease. The Stokes shift also decreases with increasing x, following which both energy positions become 1.66 eV, which is smaller than the band gap of InN (1.9 eV). These anomalous features of the optical properties of Al1−xInxN might be affected by the absorption in the infrared region caused by the high electron concentration. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125615
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  • 9
    Electronic Resource
    Electronic Resource
    Paleolimnological investigation of recent acidity changes in Sawanoike Pond, Kyoto, Japan (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 285-304 
    Details
    ISSN: 1573-0417
    Keywords: paleolimnology ; acidification ; sediment chemistry ; diatoms ; metals ; spheroidal carbonaceous particles ; pollen ; radionuclides ; Japan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sawanoike Pond, an artificial reservoir constructed ca. 150 yrs. ago, lies in an area geologically sensitive to acidification and contains water that is presently weakly acidic (pH 5.5; alkalinity 15 μeq 1-1). Sediments from a core obtained from the northern part and a core from the central part of the pond were analyzed for organic matter, total organic carbon, total nitrogen, natural and artificial radionuclides, pollen, diatoms, metals and spheroidal carbonaceous particles. A peaty silt layer at the bottom of the central core was replaced by a silt layer initially rich in humic substances, but became more mineral-rich near the surface. Although most of the dominant diatoms throughout the cores were acidophilous taxa, some acidobiontic species increased moderately in abundance after the middle 1960's. Diatom-inferred pH values for the northern core are relatively low before about 1930, then increase, reaching a maximum level between the 1930's and the late 1940's. They then decrease to the surface and reach minimum level during the middle 1980's. Diatom-inferred pH declined by 0.4-0.5 units in the northern core and 0.2-0.3 units in the central core since ca. 1910, when vegetation around the shore changed to a community similar to that of recent years. An increase in labile Pb, Zn, Cd and spheroidal carbonaceous particles, indicative of atmospheric deposition of fossil fuel combustion by-products, preceded the decline in inferred pH. The inferred pH decline of the pond could be an acidification due to acidic precipitation caused by fossil fuel combustion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008199830698
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  • 10
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    Structural properties of InN on GaN grown by metalorganic vapor-phase epitaxy (1999)
    American Institute of Physics
    Details
    Publication Date: 1999-06-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics
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